Broaching tool



H. w. JESPERSEN 2,651,102

BROACHING TOOL Sept 8, 1953 Filed June 8, 1949 ,r l i e ATTQRNEY Patented Sept. 8, 1953 I BROACHING Tool.

Helge W; Jespersen, Western Springs, 111., as-

signor to Western Electric Company, Incorpo- Y., a corporation of New rated, New York, N. York ,Application June 8, 194 9, Serial No. 97,827. 1 5 Claims. (Cl. 29-951) This invention relates to a breaching tool and to a method of making the same.

In the manufacture of certain articles such, for example, as the magnet structures of electrical measuring instruments, a high degree of precision is required and, accordingly, difiiculties are encountered in forming cooperating surfaces of the magnet structures which define the air gap of the completed instruments. Numerous breaches have been designed for breaching meter magnet assemblies and Patent 2,394,723 issued to S. J. Snorek discloses one type of breach which unitary structure would be advantageous from a manufacturing standpoint.

In cases where a one-part breach is used it is necessary in order to produce two concentric surfaces to grind away a part of the cutting surfaces of the breach. It has heretofore been the practice to remove these surfaces by grinding or milling in the direction of the axis of the breach while at the same timeretating the breach back and forth on its axis through an angle substantially equal to the are it was desired to grind. Such a procedure has proved to be inaccurate primarily due to the fact that any grinding surface will wear slightly between the time the grinding operation starts at one side of the arc and the time the grinding has progressed, by the rotation of the breach on its axis, to the other extreme of the arc. Consequently, the ground surface, which in most cases serves as a guide surface, is not absolutely concentric with the remaining cutting or breaching surface.

t is an object of this invention to provide a new and improved breach for breaching concentric surfaces.

In accordance with one embodiment of the invention, a breach is provided wherein a plurality of groups of concentric cutting or breaching surfaces of varying sizes are formed on a piece of stock by the use of a turning lathe. By using a turning lathe, absolute concentricity of all of the cutting surfaces is insured. With a tool body thus formed a part of the arcs of the larger cutting surfaces are then removed to render the corresponding arcs of smaller cutting surfaces in the groups effective without performing any grinding or cutting operation that will affect any cutting or guiding surface which might r 2 jeopardize the concentricity of the breaching surfaces; Such a breach is provided in this invention by turning concentric cutting surfaces on a lathe and then milling or grinding through the larger of the cutting surfaces in a direction transverse to the axis of the breach to leave exposed the cutting edges of the smaller diameter. Thus, no'portionof the breach that will ultimately come in contact with the material being broached is affected by the grinding or milling operation. V

A more complete understanding of the invention may be had by referring .to the following description when read in conjunction with the accompanying drawing wherein:

Fig. 1 is a side elevationof one type of breach embodying the principles of the invention;

Fig. 2 is a cross-,sectionalview taken along line 2--2 of Fig. 1; and

Fig. 3 is an elevational view of a magnet structure which may be formed by the breach of Figs. 1 and 2.

Referring now to Figs. 1 and 2, the breaching tool comprises a shaft portion I I having a notch I2 therein for attaching the breach to any suitable broach operating mechanism. Intermediate its ends the breach has a series of groups of teeth I3, Idcut in it by means of a turning lathe, and initially these teeth extend completely around the circumference of the tool. The tooth I3 of each group is turned to a larger diameter than the next succeeding teeth 54 of each group; therefore it is obvious that only the teeth I3 would be effective unless portions of the teeth l3 wereremoved. .In order to breach two concentric surfaces the, necessary portions of the arcs of teeth I3 are milled or ground away by passing the breach over 'a milling or grinding machine, the milling or grinding being carried out in a direction normal tothe axis of the breach. Suchan'operation results in the removal of the desired portion of the cutting tooth I3 torender the corresponding arcuate cutting surface of the tooth I4 effective. The particular ground or milled surface which is indicated at I5 may be of any suitable depth depending on the length of the arcs it is desired to breach, and it is obvious that whereas a milling machine will give a straight out at I5, a rotary grinding wheel which gives an arcuate shaped cut by merely moving the grinding wheel toward the center of the breach without moving the breach transversely with respect to the grinding surface would provide an equally satisfactory breach.

It is also desirable when turning the teeth of the broach to provide annular recessed portions I6, which portions serve to receive the chips removed during the breaching operation.

A broach such as shown in Figs. 1 and 2 may be used to broach two concentric suriaces, such for example as thetwo 'arcuate surfaces I1 and I8 of a meter magnet structure I9 shown in Fig. 3. The larger arcuate segment I8 in this case is formed by the broaching action of the teeth 53, and the smaller segment I? is formed' by the teeth I4. I H H Although the invention has j beei ifilhi s'tratled and described in conjunction with a brcachhaving groups of teeth arranged in pairs, it is obvious that any number of teeth could be provided in each group. In this *case stature be necessary to have each subsequent tooth each group of a smaller diameter than the preceding tooth, and each desired'areuateportion would be made efie'ctive rertrbaemn by'milling away the corresponding arcs of all of the largerteeth in the group. In "this '"r'nar'irier a lurality of concentric arcs may be preached simultaneously. I

It is also pointed out that although all of the teeth have been described and illustrated as cutting teeth, it is entirely possibleto provide burnishing orguiding surifacesin place of some of the cutting teeth under certain conditions. For example, during the final few'thousandths or an inch of the breaching operation of a ineter magnet it has beenfounddesirable to u'sethe larger arc of the magnet is 'a guide for the final broaching of the'smaller arc, in which case teeth I3 are replaced by appropriate non-cutting guiding surfaces on apartof'the preach to guide the teeth 14 in their'final cuts. M

It is further pointed out thattheteeth inach group nee'dnot be :fiush, as illustrated here, but

may bespaced from eaehtmer 'al'orig'jthe axis of the broach. It has beenfound that in broachingtwo or more concentric "surfaces simultaneously there is a, tendency for the object being broached to walk orfbecome misaligned if it is'not supported byfat'leasttwo orthree teeth of the broach" at all timesjthus it will usually be found necessary, particularly'inthe broaching of objects of smallthickne'ss, to turn'at' least a part of the teeth flush inforder to'providethe requisite support for'th'e reasons explained above.

Although "all of the'corre'spondingteeth the drawing have been shown" as being of the same diameter, it is to be understood that 'the teeth'are actually larger at the right end of the breach '(Fig. 1) since as in the case of all breaches, a

slight taper is present,ihcreasing from left'to right (Fig. 1). v

It is to be understood thatthe 'abovedescribe'd arrangements are simply illustrative of the aDP1i-- cation of the principles of the invention. Numerous other arrangements may "be readily devised by those skilled in the artwhich "will embody the principles of the invention and fall within the spirit and scope thereof.

What is claimed is:

1. The method of making a broach which comprises turning a plurality of pairs of cutting surfaces on a piece of stock, the diameter of the first of eaeh'ipair of surfaes bing laiger than the diameter ofthe secdndof each pair of surfaces, and milling away a portion of the arc of the first of each pair of cutting surfaces thereby to-feiid'er the corresponding portion of the arc of the second of each pair of cutting surfaces efifectiyeioif breaching.

V '2 rpetremee of making a broach from a piece of swampa1 includes turning a plurality of pairs of cutting surfaces on said stock, and reiiioviiig hy a 'irinding cut transverse to the axis of thestock a portion of the cutting surface of one of each pair of cutting surfaces thereby to render the corresponding portion 0;. the other cutting surface of each pair efrcaverer broacheh 3. The 'hieth'odo'f marine "a 'b'ro'a'ch ffro'n' a piece of stock"whichfincludes turning "a plurality "of "pairs oi "cutting surfaces on said stockfthe j'dija'meter of the first of each pair of surfaces being larger thahthe dia'meter ofth'e secdn'a cr Teach pair of *su'rf aces, and meme-away by a ciit transverse to the axis'b fthe'jstocl; asegnierrt ef the cutting edgeci the il'rstof each pair of cut- 'tingsurfaces thereby rndehn -the-corr'sponeing segment of the secondp ie'a'chp'air f cuttin surfaces efiective for iiroahin'g.

v 4. hej method f niaxing a breach from a piece of 'stock whichincludes-turning a 'pl-ii ity of groups of stepped {cutting surfaces 'on said "stock, :the "diameters of the-ste ped surfaces 6: each 'group being progressively smaller, and milling away "by cuts "transv'erse to the aziis "of the broach segments of 'the cutting "surfaces thereby: to rhdr"the'correspondingsegments of the "next s'r'naller unmilled cutting surfaces effecti'veiferbreachin "each of *said "second-mentioned cutters being -li'eve'd on 'on'eJSide thereof si'ifiiciently that a portion of the 1arger-endof the' first-irrentiofied cutter projects-beyond the rel ieved portion.

W."'JESPERSEN. Rter-ences Cited in the hie of t his patent UNITED STATES PATENTS Number Name Date 2,'Q"1'9l l'9l "Dra'di etal "Au'g.f4,f1936 2,120,041 Prae'g 'Junef'l, 193's 2 ,39 4,'12 3 snor k ='Fb. i2, 1M6 2,398,310 Howell Au'g.'9, 1946 

